Siloxanic proton-conducting

D-HION-APPE proton conducting materials are presented as an important development to replace the ubiquitous and costly perfluorinated ionomers currently in use. These materials can be synthesized by the copolymerization of metal alkoxides and organic-substituted silicon alkoxides or suitable oligomers. In particular, two new siloxanic proton-conducting membranes are described (Di Noto and Vittadello, 2005 Di Noto et al, 2005) ... 

Synthesis of the precursor necessary for the preparation of the siloxanic proton-conducting materials [I] and [II]. (a) Preparation of allylsulphonylchloride (b) hydrosilylation of allylsulphonylchloride and allyidimethylchlorosilane using polymethylhydrosiloxane reproduced from Di Noto and Vittadello (2005) by permission of Elsevier. 

Synthesis of the siloxanic proton-conducting polymer electrolyte [II] reproduced from Di Noto and Vittadello (2005) by permission of... 

DI NOTO V, vrrTADELLo M (2005), Two new siloxanic proton-conducting membranes Part I. Synthesis and structural characterization , Electrochim Acta, 50, 3998-4006. 

Fig. 5.22 Proton-conducting membrane based on benzyl sulphonic acid siloxane.

For the preparation of proton-conducting polymers, aminoalkyl-substituted siloxanes made by sol-gel processing of (MeO)3Si(CH2)3NR2 [for example, NR2 = NH2, NH(CH2)2NH2, NH(CH2)2NH(CH2)2NH2] were doped with CF3SO3H129. 

Figure 23.10 Proton conductivity of a few prototypical proton conducting separator materials Nafion as a representative of hydrated acid ionomers (see also Fig. 23.2(a) [43, 78], a complex of PBI (polybenzimidazole) and phosphoric acid as a representative of adducts of basic polymers and oxo-acids (see also Fig. 23.2(b)) [16], phosphonic acid covalently immobilized via an alkane spacer at a siloxane backbone (see also Fig. 23.2(c)) [127], the acid salt CsHSO, [125] and an Y-doped BaZrOj [126].

Crosslinked sulfonated poly(imide-siloxane) can be obtained by the radical grafting onto the silylmethyl group of poly(dimethylsiloxane) [59]. Large, well-connected hydrophilic domains have been detected by transmission electron microscopy that are responsible for the high proton conductivity of the membrane. The unique phase separated morphology of the membrane is responsible for the outstanding hydrolytic stability. 

Semi-interpenetrating polymer network membranes based on sulfonated polyimide-siloxane and epoxy polymers have been prepared [61]. The membranes show desirable mechanical properties and thermal stabilities, with proton conductivities superior to those of Nation 117 at 80 °C. 

The concentration of the siloxane introduced into the copolymer is most easily determined by proton NMR for soluble systems, as briefly referred to in Sect. 3.1. This was demonstrated by Summers et al. [45] and Arnold and coworkers [46-50], as well as Rogers et al. [52]. Others have routinely conducted these experiments to establish the copolymer composition. Infrared spectroscopy has been particularly useful for demonstrating the transformation of the amic acid, which is often an intermediate for the final imide form. The assignments have been noted in many of the polyimide reviews referred to earlier [1-8]. In addition, it is useful to conduct an elemental analysis for silicon as complementary proof of copolymer composition. Solid-state NMR can be used even for intractable polyimide systems to provide a good estimate of the copolymer composition. 

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